As mobile devices have been increasingly developed, and the demand for such mobile devices has increased, the demand for batteries has also sharply increased as an energy source for the mobile devices. Accordingly, much research on batteries satisfying various needs has been carried out.
In terms of the shape of batteries, the demand for prismatic secondary batteries or pouch-shaped secondary batteries, which are thin enough to be applied to products, such as mobile phones, is very high. In terms of the material for batteries, the demand for lithium secondary batteries, such as lithium ion batteries and lithium ion polymer batteries, having a high energy density, a high discharge voltage, and a high power stability, is very high.
Furthermore, secondary batteries may be classified based on the construction of an electrode assembly having a cathode/separator/anode structure. For example, the electrode assembly may be constructed in a jelly-roll (winding) type structure in which long-sheet type cathodes and anodes are wound while separators are disposed respectively between the cathodes and the anodes, a stacking type structure in which pluralities of cathodes and anodes having a predetermined size are sequentially stacked while separators are disposed respectively between the cathodes and the anodes, or a stacking/folding type structure in which pluralities of cathodes and anodes having a predetermined size are sequentially stacked while separators are disposed respectively between the cathodes and the anodes to constitute a bi-cell or a full-cell, and then the bi-cell or the full-cell is wound.
Recently, much interest has been taken in a pouch-shaped battery constructed in a structure in which such a stacking or stacking/folding type electrode assembly is mounted in a pouch-shaped battery case made of an aluminum laminate sheet because of low manufacturing costs, light weight, and easy modification in shape. As a result, the use of the pouch-shaped battery has gradually increased.
FIG. 1 is an exploded perspective view typically illustrating the general structure of a conventional representative pouch-shaped secondary battery.
Referring to FIG. 1, the pouch-shaped secondary battery 10 includes an electrode assembly 30, pluralities of electrode tabs 40 and 50 extending from the electrode assembly 30, electrode leads 60 and 70 welded to the electrode tabs 40 and 50, respectively, and a battery case 20 for receiving the electrode assembly 30.
The electrode assembly 30 is a power generating element comprising cathodes and anodes sequentially stacked while separators are disposed respectively between the cathodes and the anodes. The electrode assembly 30 is constructed in a stacking structure or a stacking/folding structure. The electrode tabs 40 and 50 extend from corresponding electrode plates of the electrode assembly 30. The electrode leads 60 and 70 are electrically connected to the electrode tabs 40 and 50, extending from the corresponding electrode plates of the electrode assembly 30, respectively, for example, by welding. The electrode leads 60 and 70 are partially exposed to the outside of the battery case 20. To the upper and lower surfaces of the electrode leads 60 and 70 are partially attached insulative films 80 for improving sealability between the battery case 20 and the electrode leads 60 and 70 and, at the same time, for securing electrical insulation between the battery case 20 and the electrode leads 60 and 70.
The battery case 20 is made of an aluminum laminate sheet. The battery case 20 has a space defined therein for receiving the electrode assembly 30. The battery case 20 is formed generally in the shape of a pouch. In the case that the electrode assembly 30 is a stacking type electrode assembly as shown in FIG. 1, the inner upper end of the battery case 20 is spaced a predetermined distance from the electrode assembly 30 such that the plurality of cathode tabs 40 and the plurality of anode tabs 50 can be coupled to the electrode leads 60 and 70, respectively.
FIG. 2 is a partially enlarged view illustrating the inner upper end of the battery case of the secondary battery shown in FIG. 1, in which the cathode tabs are coupled to each other in a concentrated state and connected to the cathode lead, and FIG. 3 is a front see-through view illustrating the secondary battery of FIG. 1 in an assembled state.
Referring to these drawings, the plurality of cathode tabs 40, which extend from cathode collectors 41 of the electrode assembly 30, are connected to one end of the cathode lead 60, for example, in the form of a welded bunch constituted by integrally combining the cathode tabs 40 with each other by welding. The cathode lead 60 is sealed by the battery case 20 while the other end 61 of the cathode lead 60 is exposed to the outside of the battery case 20. Since the plurality of cathode tabs 40 are integrally combined with each other to constitute the welded bunch, the inner upper end of the battery case 20 is spaced a predetermined distance L1 from the upper end surface of the electrode assembly 30, and the cathode tabs 40 combined in the form of the welded bunch are bent approximately in the shape of a V. Accordingly, the coupling regions between the electrode tabs and the corresponding electrode leads may be referred to as “V-form regions.”
However, such V-form regions have a problem in the aspect of safety of the battery. Specifically, when the battery drops with the upper end of the battery, i.e., the cathode lead 60 of the battery, down, or an external physical force is applied to the upper end of the battery, the electrode assembly 30 moves toward the inner upper end of the battery case 20, or the upper end of the battery case 20 is crushed. As a result, anodes (not shown) of the electrode assembly 30 are brought into contact with the cathode tabs 42 or the cathode lead 60, and therefore, a short circuit may occur inside the battery. Consequently, the safety of the battery is greatly lowered.
As an example of a technology for preventing the occurrence of such an internal short circuit of the battery, Korean Utility Model Registration No. 0207948 discloses a lithium ion polymer battery including a battery case for receiving a battery cell and electrode tabs, the battery case being constructed in a structure in which the battery case wraps the battery cell and the electrode tabs in a sealing fashion and sides of the battery case are inclined such that the area of the battery case is increased from the bottom to the top of the battery case, wherein cathode plates, anode plates, and separators, included in the battery cell, are formed with different sizes such that the cathode plates, the anode plates, and the separators are located adjacent to the inner parts of the inclined sides of the battery case. However, this technology has a drawback in that it is required to manufacture the cathode plates, the anode plates, and the separators with different sizes, whereby the manufacturing process is complicated, and the costs of equipment are increased. For this reason, this technology has no practical use.
Also, Japanese Patent Application Publication No. 2001-052659 discloses a stacking type polymer electrolyte battery characterized in that, at a region where electrode terminals are received, the depth of a sheathing container is gradually decreased outward from a region where an electrode assembly is received. However, this technology has a drawback in that a contact region between the electrode assembly and a battery case is loosened due to the expansion and contraction of the battery case caused by the repetitive charge and discharge of the battery, and therefore, when external impacts are applied to the battery in this state, a short circuit may occur in the battery.
In addition, Japanese Patent Application Publication No. 2005-116482 discloses a thin battery including an sheathing member which has a flat surface previously formed at a region where an electrode assembly is received and an inclined surface previously formed between the flat surface and the outer circumferential surface of the sheathing member, thereby accomplishing uniform surface pressure distribution and reducing the volume of the battery. However, this technology still has the above-mentioned drawback.
Consequently, there is a high necessity for a technology that is capable of not only preventing the occurrence of an internal short circuit of a battery due to the dropping of the battery or the application of an external force to the battery but also preventing the occurrence of an internal short circuit of the battery even when the battery case somewhat swells due to the repetitive charge and discharge of the battery.